Vehicle headlamp with a lens having elements formed on a boundary surface therefor

ABSTRACT

There is presented a vehicle headlamp with an imaging optics that is designed to project, as light/dark boundary, into the area in front of the vehicle headlamp, an edge that delimits a light flux of a light source of the vehicle headlamp, a boundary surface of a component of the imaging optics, through which the light flux penetrates, having an overhead element in the form of a local deformation of the boundary surface having a prismatic effect by means of which the light is deflected into an overhead area lying over the light/dark boundary. The vehicle headlamp is distinguished by the fact that the boundary surface has more than one hundred overhead elements distributed discretely over the boundary surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to German patent applicationserial number 10 2009 020 593.4, which was filed on May 9, 2009, whichis incorporated herein in its entirety, at least by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle headlamp according to thepreamble of claim 1. Such a vehicle headlamp is disclosed in utilitymodel G 90 00 395.

2. Description of Related Art

Specific location-dependent illuminances are required for vehicleheadlamps in the SAE legal sphere. These are prescribed separately forlow beam light and high beam light with the aid of numerous measurementpoints. Alongside prescribed illuminances of the low beam lightimpinging on the road, that is to say below the so-called light/darkboundary, there is also a need to meet special requirements above thelight/dark boundary. This area of the light distribution is denoted asoverhead or sign light area, the latter term being derived from thevisibility of traffic signs. The legal measuring points of the so-calledoverhead light extend up to four degrees above a line that marks thehorizon, and are characterized by minimum values and maximum values ofthe lighting intensities permissible there.

In the case of reflection systems, the measuring points can be veryeasily catered for with minimum values by a suitable shaping of thereflector. Projection systems with a low beam light function light thearea above the light/dark boundary only very weakly, because of theiroptical principle. Consequently, it is necessary in the case of theseprojection systems to take measures to meet the minimum values of theintensities in this area. This can be achieved, on the one hand, bymeans of additional, reflecting components in the projection system suchas, for example, reflecting diaphragms. Thus, it is known to make use ofadditional sheets that are arranged horizontally in the beam path andare strongly reflecting at high incidence angles. Said additional sheetsconstitute an additional component and therefore undesirably causehigher costs and a greater system complexity.

Other solutions provide a local change in geometry within the projectionlens that exerts a suitable prismatic effect on a portion of the lightflux penetrating through the lens.

The vehicle headlamp disclosed in utility model G 90 00 395.0 has animaging optics with a lens and a diffusion lens that serves well astransparent cover of the vehicle headlamp. In order to suppress a colorfringe, the light exit boundary surface of the lens is dividedhorizontally into an upper aspheric segment and a lower asphericsegment. At the transition between the two segments, the lens has a partof a horizontally arranged convex cylindrical lens. This cylindricallens upwardly deflects the portion of the lens light flux thatpenetrates the cylindrical lens into a defined angular range such thatthis deflected light flux lights the overhead area.

In the case of another configuration, a sector of a horizontallyarranged concave cylindrical lens is integrally formed on the lightentrance boundary surface of the diffusion lens. This cylindrical lenslikewise directs upward the partial light bundle traversing it. Afurther configuration specifies that it is also possible to provide aplurality of cylindrical lenses one above another vertically on thediffusion lens. The overall aim in the case of the known vehicleheadlamp is to enable the upwardly deflected partial light bundle tofulfill legally required light values for fog lamps above the light/darkboundary.

Further examples of local deformations of the lens surface of theprojection lens which, owing to their additional prismatic action,deflect light into measuring points within an overhead area aredisclosed in the publications DE 10 2004 024 107 A1 and U.S. Pat. No.6,971,778. DE 10 2004 024 107 A2 discloses for this purpose a lens witha cylindrical section running horizontally in the middle. U.S. Pat. No.6,971,778 exhibits in this context a local depression in the lowerregion of the lens. Also known are geometric surface modificationswhich, however, do not primarily aim at producing defined overheadintensity values. These include, for example, lenses with horizontallyand obliquely running corrugated structures. Such a lens is disclosed inDE 40 31 352 A1.

A great disadvantage of the known solutions, which operate with a localdeformation of the lens surface, resides in the fact that they all reactsensitively to even a slight change in the light distribution.Consequently, given the occurrence of a series of manufacturingtolerances, markedly altered illuminances can occur in the range of thesign-light measured values. The consequence is that it cannot be ensuredthat an overhead solution can be used on another projection system (thatis to say in the event of a change in light distribution). This means,in turn, that it is necessary as a rule to find for each projectionmodule new solutions to the production of the prescribed overheadlighting intensity values.

It is also disadvantageous that the required prismatic action alwaysconstitutes a clearly visible incursion into the lens surface that marksits appearance. In the case of previously disclosed solutions, this ispartly felt as unaesthetic, or the local deformations are perceived asdefects in the projection lens. Thus, various overhead solutions areperceived as conchoidal fractures (instances of splitting), glassdefects such as inclusions and bubbles or visible jumps in the lens (forexample in the case of horizontally arranged cylindrical lenssectors)—all of these being typical of glass.

BRIEF SUMMARY OF THE INVENTION

Against this background, the object of the invention is to specify avehicle headlamp of the type named at the beginning in the case of whichthe desired deflection of light into the overhead area lying above thelight/dark boundary reacts less sensitively to slight changes in thelight distribution, and which is, moreover, not falsely perceived asdefective by the final customer.

This object is achieved with the aid of the features of claim 1. As inthe case of the prior art, the overhead lighting is obtained by thelight-deflecting, and thus prismatic action of local deformations. Incontrast to the prior art, where use is made only of cylindrical lensesthat are large or less so, are respectively coherent and traverse theentire lens surface, the invention provides a distribution of thedeflecting structures over more than 100 overhead elements, and theirdiscrete arrangement, that is to say one in which they are respectivelyspatially separated from one another, on a boundary surface throughwhich the light flux moves. There can also be more than 1000 overheadelements. The number of the overhead elements is therefore higher by oneto three powers of ten than in the case of the prior art. Eachindividual overhead element can therefore turn out to be correspondinglysmaller. The subjective impression of a lens defect is avoided owing tothe reduction and the discretely distributed arrangement. Moreover,production tolerances in the dimensions of the individual overheadelements do not have such a disturbing effect as in the case of theprior art. The overhead light is lent a lesser sensitivity to thesetolerances by the large number of the overhead elements.

These desired effects are additionally amplified by an arrangement ofthe overhead elements in a uniform distribution on the boundary surface.The uniform distribution can relate to subregions of the boundarysurface, or else to the entire boundary surface. In other words, theuniform distribution of the overhead elements also lends the overheadlight a lesser sensitivity to these tolerances.

It is preferred for the overhead elements to be distributed over theentire light exit surface. It is also preferred for the overheadelements to be aligned perpendicularly with respect to the boundarysurface in such a way that the resulting deflection angles in the lightare the same relative to the optical axis for each overhead element.

The particularly high insensitivity achieved in the case of a uniformdistribution of identically shaped overhead elements with respect tochanges in the light distribution yields not only an increasedinsensitivity to manufacturing tolerances, but also yields afurther-reaching ability to use the structured boundary surface inprojection systems of other vehicle headlamps such that a reliableboundary surface design can be used without complicated changes in thecase of other vehicle headlamps.

Overall, in each case on their own and in combination with one anotherthese features render it possible to produce an overhead lighting in adefined way. The sign-light values produced can be set in a way definedby number, area and geometry of the overhead elements, and can beeffectively accessed for simulating dimensioning.

It is preferred in this case for the sum of the areas of the overheadelements of a boundary surface to have a value of between five percentand ten percent of the value of the boundary surface. The legalstipulations can be fulfilled by this dimensioning.

A further advantage of the uniform distribution resides in the fact thatthe latter is compatible with other uniform structurings of the boundarysurface. Such a periodic structuring serves the purpose, for example, ofmaking a light/dark boundary often felt to be acutely disturbing in thecase of projection systems appear less sharply defined, that is to sayappear to have a more continuous transition of the light intensitybetween the light and the dark areas. The overhead elements presented inthis application can be embedded periodically in a periodicmicrostructure, it being preferred to provide in each case roundedtransitions between elements of the microstructure and the overheadelements. The rounded transitions are preferably fashioned such that, touse mathematical terminology, they can be continuously differentiated atleast once. This applies analogously for configurations without amicrostructure, in the case of which the overhead elements merge inrounded fashion into the remaining boundary surface.

Disturbing optical effects are avoided because of the result that thesurface is free from edges. Moreover, the production of tools with whichthe boundary surfaces are produced is simplified and the service life ofthe tools is lengthened.

Further advantages follow from the subject matters of further dependentclaims, the description and the attached figures.

It goes without saying that the features named above and still to beexplained below can be used not only in the respectively specifiedcombination, but also in other combinations or on their own withoutdeparting from the scope of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a vehicle headlamp as technical field of the invention.

FIG. 2 shows an illustration of a refinement of a light module of thevehicle headlamp according to FIG. 1, in a longitudinal section.

FIG. 3 shows various views of an optical lens of the light module fromFIG. 2 with an exemplary embodiment of the invention.

FIG. 4 shows a perspective view of an individual overhead element of thelens from FIG. 3.

FIG. 5 shows a cross section of such an overhead element in conjunctionwith a light flux.

FIG. 6 shows light distributions that result in the case of a vehicleheadlamp with and without the use of overhead elements.

DETAILED DESCRIPTION OF THE INVENTION

In detail, FIG. 1 shows a vehicle headlamp 1 with a housing 2illustrated as a cuboid, a transparent cover pane 2.1, at least onecontrol unit 17, and a bend light module 3 that can be pivoted about ahorizontal axis 4 in the housing 2.

The bend light module 3 has a support frame 5, a light module 6, a firstcontrol unit 7, a first motor 8 and a gearbox 9 which, together, form anassembly. Here, the light module 6 is mounted in the support frame 5such that it can rotate about a vertical axis. Motor 8 and gearbox 9 areconnected, on the one hand, to the stationary support frame 5 and, onthe other hand, to the light module 6, and are thus capable of exertingan adjusting torque between support frame 5 and light module 6.

The light module 6 has at least one light source and an optical element,such as a lens, that focuses the light flux of the light source, whichis collected by a reflector or a primary optics, and directs it along alighting direction 10 into the area in front of the vehicle headlamp 1.

The light source is preferably a gas discharge lamp, for example a xenonlamp, a semiconductor light source, for example an arrangement oflight-emitting diodes (LEDs), or a halogen lamp.

The at least one light source is situated approximately at the firstfocal point of an ellipsoidal reflector. So-called polyellipsoidalreflectors are preferred. The diaphragm, which is imaged by the lens, islocated approximately at the second focal point of the reflector. Thelens images the diaphragm upper edge on the roadway. The optical axis ofthe light module corresponds to the optical axis of the lens. The focalpoints of the ellipsoidal reflector lie on the optical axis of the lightmodule. The object focal point of the lens is situated in the region ofthe diaphragm. The light distribution can be influenced by varying thediaphragm upper edge.

Particularly in conjunction with semiconductor light sources, alongsidesaid elliptical reflectors use is also made of transmitting systems inwhich the light is focused at the second focal point by refraction, butalso partly by total internal reflection (attachment optics).

The reflector and the attachment optics are denoted below as primaryoptics, and the lens as secondary optics.

Low beam lighting systems of long range (illuminance) and lowcounter-traffic dazzling can thereby be illustrated. The secondaryoptics is preferably designed as an individual aspheric lens with focallengths of between 40 mm and 75 mm. For technical lighting reasons, thelenses can have at least partially a regularly or irregularly structuredsurface. These structures have a height of approximately 3 μm-30 μm inrelation to the base surface of the lens, and serve to influencebrightness gradients of the light/dark boundary and/or to influencecolor effects in the imaging of the diaphragm upper edge. Irregularstructures are comparable to the surface of an orange peel. However,random structures such as can be produced, for example, by sandblastingor shot peening are also possible. These structures constitute aneffective but less flexible method for influencing said properties.

A targeted setting of the light/dark boundary can be achieved with aperiodic array, at least partially covering the aspheric surface of thelens, of identical or similar individual optical elements. Inparticular, the light/dark boundary can be influenced in a targetedfashion by a suitable surface of the structural elements. These elementsare described in the as yet not disclosed DE 10 2008 023 551 of theapplicant.

Said structures can now be combined with the overhead elements. By meansof an appropriate configuration of the structural elements, the overheadelements can replace a portion of the regular structural elements.

For the purpose of aligning the lens correctly in rotary fashion,markings are introduced at the lens edge, or else positive codings withthe lens holders.

Various diaphragm mechanisms can be used in order to produce variouslight distributions such as, for example, low beam light, high beamlight, town light, rain light etc. By way of example, switching overbetween low beam light and high beam light can be achieved with the aidof a folding diaphragm in the case of which the high beam lightdistribution is achieved by folding the diaphragm about a horizontalaxis that runs perpendicular to the driving direction. In a preferreddesign, use is made of a diaphragm roller that is mounted so as torotate about an approximately horizontal axis and has various contourson its periphery which, when projected onto the road by the secondaryoptics, can form various light/dark geometries. An alternativerefinement provides a diaphragm arrangement with one or more diaphragmelements that are adjustably mounted in a vertical or in anapproximately vertical direction. These diaphragms can be verticallyadjusted via a second motor 11 and a gearbox in conjunction with slottedlink guide or cam plate gear mechanisms. The gearbox can be the gearbox9 or a separate gearbox.

The various positionable diaphragms produce different light/darkgeometries that are projected by the secondary optics onto the road, itbeing possible as a result to provide different low beam lightfunctions. In a preferred design, parts of the slotted link guide or camplate gear mechanisms are integrally formed directly on the diaphragms:for example, slotted guide curves, cams or rollers.

If a gas discharge lamp or a semiconductor light source is used as lightsource, it is possible to provide a control unit, for example thecontrol unit 7, to control the energy supply of these light sources. Asan option, the control unit 7 can also include electronic elements forthe electric drive of the motors 8 and/or 11 and 16.

The light module 6 is mounted in the support frame 5 such that it canpivot about a vertical axis 12. In the refinement illustrated, apivoting movement is driven by the first motor 8 via a horizontalpivoting mechanism, arranged in the gearbox 9, and a lever mechanism 13that couples a drive shaft 14.1 of the horizontal pivoting mechanism tothe support frame 5. It holds overall that the light module 6 and thesupport frame 5 are coupled by motor via the first motor 8 and via thegearbox 9.

The support frame 5 is, for its part, connected in a fashion secureagainst rotation to the horizontally running axis 4, which is actuatedin the schematic refinement illustrated via a vertical pivotingmechanism 15, fitted outside on the housing 2, and a third motor 16. Thethree motors 8, 11 and 16 are preferably electric motors, in particularstepping motors, and are actuated by one of the control units 7 or 17.

The light module 6 therefore has a universally joined suspension. It ispreferred in this case for the point of intersection of the pivot axesto lie at the center of the envelopes of the outer contour of the lens.

The first motor 8 is driven to pivot the light module 6, and thus thelighting direction 10, in a horizontal direction. In a preferredrefinement, the motor 8 is controlled by the control unit 17 as afunction of a steering angle of steerable wheels of the motor vehiclesuch that the lighting direction 10 follows the steering angle of thesteerable wheels. The drive of the third motor 16 varies a verticalcomponent of the lighting direction 10 and serves, for example, tocontrol the lighting range.

FIG. 2 is a schematic of a refinement of the light module 6 in alongitudinal section. The light module 6 has a light source 18 foremitting light beams, and a reflector 20 for reflecting at least aportion of the emitted light beams. The reflector 20 is preferablyformed as an ellipsoid of revolution, or an ellipsoidal freeformdeviating therefrom. The light source 18 is arranged at a first focalpoint F₁ of the reflector 20. A diaphragm arrangement 22 shields atleast a portion of the light flux emanating from the reflector 20. Thediaphragm 22 is preferably arranged in a plane that runs perpendicularto an optical axis 24 and through the second focal point F₂ of thereflector 20.

A lens 26 is fastened on a front edge of the reflector 20 by means of alens holder (not illustrated) acting on a collar 28. The lens 26consists of any desired optically transparent material, for example of athermally stable plastic or glass, and has a substantially flat lightentrance boundary surface 30 on the side facing the light source 18, anda convex light exit boundary surface 32 on its opposite side. Of course,the boundary surface 30 can also be of concave or convex design.

The light module 6 serves to produce a light distribution with alight/dark boundary, preferably a low beam light distribution or a foglight distribution. The light/dark boundary is produced as a projectionof the upper edge of the diaphragm arrangement 22 in the lightdistribution produced on the roadway by the light module 6. Thedirection x is substantially parallel to the direction 10 of the lightflux and, when the headlamp 1 is installed, parallel to the longitudinalaxis of the vehicle. The z-direction is parallel to the vertical axis ofthe vehicle and points upward. The y-direction is correspondinglyperpendicular to the plane of the drawing, and points into the latter.

The optical lens 26 is illustrated in a perspective view in FIG. 3 a,and in a plan view in FIG. 3 b. It goes without saying that thenumerical values specified in millimeters [mm] on the x-, y- and z-axesare given merely as examples and are in no way to be understood asrestrictive.

FIG. 3 b shows a plan view, taken against the light exit direction 10,of the light exit boundary surface 32 of a lens 26 that has more thanone hundred overhead elements 34 distributed discretely over theboundary surface 32. In the refinement illustrated, approximately twohundred and twenty such overhead elements 34 are distributed uniformlyover the boundary surface 32. Here, a uniform distribution is understoodas a distribution in the case of which the projections of the overheadelements in the y-z-plane form a periodic two-dimensional latticestructure. The overhead elements appear equally large in thisprojection.

FIG. 3 b shows a refinement in the case of which the overhead elements34 are distributed over the entire light exit boundary surface 32 of thelens 26. It is also possible to undertake a uniform distribution only ina subregion, for example in a circle that is concentric with theperiphery of the lens 26 and has a smaller radius. In principle, theoverhead elements 34 can, however, be arranged in various arrangements,for example in concentric circles, spirals, rhombuses, triangles orother patterns such as logos. Furthermore, for the purpose of deflectingthe light, the individual overhead elements 34 can be arranged in simpleCartesian grids, or Cartesian grids lying one over another in offsetfashion, said grids being of different spatial frequency.

The visual appearance can be adapted by the arrangement to thesubjective aesthetic notions. The quantity of the overhead lightproduced is set by varying the packing density, the size and the shapeof the individual overhead elements 34. In any case, it is essential tothe arrangement that the individual overhead elements 34 be alignedrelative to one another such that they deflect the light in the samedirections in each case. It is also preferred to this end that theindividual overhead elements 34 have the same shape and, if appropriate,additionally the same dimensions, that is to say are the same as oneanother. The summed area of the overhead elements 34 is preferably fivepercent to ten percent of the lens boundary surface 32.

FIG. 4 shows a refinement of an overhead element 34 in a perspectiveillustration. The illustrated overhead element 34 rises out of theremaining boundary surface 32. The height of the bump over the remainingboundary surface 32 is preferably 3% to 15% of the vertical extent(length) of an overhead element. The vertical extent or length of theoverhead element is understood here as the spacing of the points 38 and40 in FIG. 5. Given the preferred dimensions of 0.5 to 4 mm, bumps of 15micrometers to 0.6 mm are obtained. The height to be selected is also afunction of the refractive index of the lens. The larger the refractiveindex, the smaller the height will be. As is to be seen from FIG. 4, thelifted out overhead element 34 respectively merges in rounding offfashion into the remaining boundary surface 32, and so no edges areproduced between the boundary surface 32 and the overhead element 34projecting therefrom in the light exit direction 10.

Various rounding surfaces defined by mathematical functions can be usedfor the rounding off, for example surfaces defined by spline functions.Rounding surfaces defined in other ways are also possible. It isessential in each case that no edge be produced.

A plan view of the overhead element 34 illustrated in FIG. 4 reveals atrapezoidal basic shape of the bump. The width of the overhead element34 in the y-direction decreases with increasing extent in thez-direction.

The overhead element 34 is implemented as a tilting of a subregion ofthe boundary surface 32 relative to the remaining boundary surface 32.This tilting results in the desired prismatic, that is to saylight-deflecting effect with which the overhead illumination isproduced. In one refinement, the tilted sections are square; however,they can also have another shape, for example said trapezoidal shape. Itis also preferred for the tilting of the surface not to be constantwithin an overhead element 34, but for it to vary in the z-direction.The degree of the tilting influences the angle by which the light isdeflected. The variation of this angle results in an illumination of theentire overhead measuring range in which it is necessary to reach and/orfall below prescribed intensities at prescribed measuring points. Theresult is thus a light band above the light/dark boundary that is litcontinuously over its area. Since the extent of the tilting determinesthe deflection angle and since, at a specific tilt angle, the width ofthe overhead element 34 influences the quantity of the light deflectedby the associated deflection angle, the quantity of the light deflectedin specific directions can be controlled by varying the width as afunction of the tilt angle. It can therefore be advantageous also to useother shapes than squares for the plan view of the overhead elements.

In a preferred refinement, the tilted region of the surface sections isimplemented by cylindrical sections or toric surface elements.Alternatively, however, it is also possible to use spline functions orcomparable mathematical functions or a combination of such functions.

Overall, FIG. 4 therefore shows in particular a refinement of anoverhead element that consists essentially of a main deflecting surface33 tilted out of the boundary surface 32 of the lens and, respectively,of at least three surfaces 35 tilted in another direction. Here, atilted surface pointing in the positive y-direction is denoted by thereference numeral 35. In the refinement illustrated, another tiltedsurface points by way of example in the negative y-direction, while yeta further tilted surface points by way of example in the positivez-direction. All three surfaces 35 tilted in another direction mergecontinuously into the main deflecting surface 33 and the boundarysurface 32. It is preferred in this case for the surfaces respectivelyto merge into one another in a continuously differentiable fashion. Inone refinement, a base surface of the lens having no bumps ordepressions is regarded as boundary surface. Alternatively, however, itis also possible to regard as boundary surface a boundary surface havingother bumps and/or depressions such as is used, for example, to reducethe contrast of a light/dark boundary.

FIG. 5 shows a cross section through the overhead element 34 of FIG. 4along the line VV in FIG. 4. The cross section of the overhead element34 is divided into a first section 42, which is situated between thepoints 38 and 40, and a second section 46 that is situated between thepoints 40 and 44. Here, the vertical extent or length of the overheadelement is understood as the spacing of the points 38 and 40 in FIG. 5.The curvature of the first section 42 corresponds in a preferredrefinement to the curvature of a lateral cylinder surface. The surface,associated with the section 42, of the overhead element 34 correspondsto a portion of a lateral surface of an imaginary cylinder whose axis issituated parallel to the base surface of the vehicle within the lens 26when the headlamp 1 is installed in the vehicle. Alternatively, thecontour 42 can also be produced as a spline function or as a comparablemathematical function or as a combination of such functions. What isessential in each case is the continuously differentiable profile for acurvature that is variable in the z-direction.

The first section 42 produces the desired low beam effect. Section 46serves only to implement a continuously differentiable, and thusedgeless transition between the first section 42 of the overhead element34 and the remaining boundary surface 32 of the lens 26.

The desired deflecting effect is made clear by comparing the lightbundle 48, which penetrates the boundary surface of the lens 26 in theregion of the overhead element 34, with the light bundles 50, 52 whichpenetrate through regions of the boundary surface 32 which are adjacentto the overhead element 34. By comparison with the deflection of thelight bundles 50 and 52, which is absent or only comparatively weak,upon penetration through the boundary surface 32, a portion 48′ of thelight bundle 48 experiences a comparatively stronger deflection in thez-direction. Owing to the comparatively stronger deflection, the lightbundle 48′ is deflected beyond the light/dark boundary, while theportion 48″ of the light bundle 48 is deflected into the low beam lightdistribution. The light bundles 50, 52 light the region below thelight/dark boundary.

In accordance with the division of the surfaces of the overhead elements34 and the remaining light exit boundary surface of the lens 26, fivepercent to ten percent of the light penetrating through the lens 26 isscattered into the overhead area, while the remaining ninety to ninetyfive percent serves to light the area beneath the light/dark boundary.

In a preferred refinement, a maximum deflection of a light beam 48,deflected by an overhead element 34, in relation to a neighboring lightbeam 50, 52 that is not deflected by the overhead element 34 is at leastfive degrees.

Up to here, the invention has been explained by way of example of alight exit boundary surface of a projection lens 26. Alternatively or inaddition, the spatially selectively deflecting effect can, however, alsobe produced by appropriately configuring the light entrance boundarysurface of the lens 26. In the case of vehicle headlamps, whose lightmodule 6 cannot be pivoted, the deflecting effect can also beimplemented, if appropriate, by distributing overhead elements over thelight entrance the boundary surface of the cover pane. However, asolution is preferred in which the overhead elements are distributeddiscretely over the light entrance boundary surface or light exitboundary surface of the projection lens 26.

FIG. 6 shows a comparison of light distributions that result in the caseof projector type vehicle headlamps with and without overhead elements.Such light distributions result, for example, on a surface arranged infront of the vehicle and aligned perpendicular to the vehiclelongitudinal axis. The horizontal line HH marks the position of ahorizon, while the vertical line VV divides the field of view of thedriver approximately in the middle of the vehicle. Points that lie onthe same curve are distinguished by a mutually identical lightingintensity. As regards a plurality of curves, the intensity decreasesoutward from inside.

FIG. 6 a shows a typical low beam light distribution of a firstprojector type vehicle headlamp without overhead elements. The lightingintensities are concentrated substantially on the area below the horizonHH.

By contrast, FIG. 6 b shows a typical light distribution such as isobtained with a second headlamp that differs from the first projectorheadlamp only by a lens 26 provided with overhead elements of the typepresented here. The lines of equal lighting intensity that bulge outwardand upward beyond the horizon represent the desired overhead lighting inFIG. 6 b. This overhead lighting, which is known per se, can be set withthe aid of the invention with the advantages, presented further above,of the insensitivity to changes in the fundamental light distributionand the improved appearance.

The invention claimed is:
 1. A vehicle headlamp, comprising; a lightsource emitting a light flux; an imaging optics projecting the lightflux into an area in front of the vehicle headlamp; a diaphragm arrangedbetween the light source and the imaging optics, the diaphragm having anedge that delimits the light flux of the light source of the vehicleheadlamp creating a light/dark boundary of the light flux projected bythe imaging optics; a boundary surface of the imaging optics throughwhich the light flux penetrates, the boundary surface having a pluralityof overhead elements in the form of a local deformation of the boundarysurface each having a prismatic effect by means of individual surfaceswhich deflect the light into an area lying over and below the light/darkboundary; wherein each overhead element has at least one surfacedeflecting a first amount of the light over the light/dark boundary andone surface deflecting a second amount of the light below the light/darkboundary and the boundary surface has more than one hundred overheadelements distributed discretely over the boundary surface.
 2. Thevehicle headlamp as claimed in claim 1, wherein the overhead elementsare distributed uniformly over the boundary surface.
 3. The vehicleheadlamp as claimed in claim 1, wherein the overhead elements aredistributed over the entire boundary surface.
 4. The vehicle headlamp asclaimed in claim 1, wherein the overhead elements are superposed on asurface structure.
 5. The vehicle headlamp as claimed in claim 1,wherein the overhead elements replace structural elements of a regularsurface structure.
 6. The vehicle headlamp as claimed in claim 1,wherein the overhead elements are the same as one another.
 7. Thevehicle headlamp as claimed in claim 1, wherein the proportion of thesum of the areas of the overhead elements of a boundary surface has avalue of between 5% and 10% of the area of the boundary surface.
 8. Thevehicle headlamp as claimed in claim 1, wherein the overhead elementsare implemented as bumps on the boundary surface.
 9. The vehicleheadlamp as claimed in claim 1, wherein the overhead elements rise 15micrometers to 0.6 mm high over the undeformed boundary surface.
 10. Thevehicle headlamp as claimed in claim 1, wherein the surfaces of theoverhead elements are implemented as tilting of subregions of theboundary surface in relation to the remaining boundary surface.
 11. Thevehicle headlamp as claimed in claim 10, wherein the imaging optics is alens and each overhead element consists essentially of a main deflectingsurface tilted out of the boundary surface of the lens and,respectively, of at least three surfaces tilted in another direction,the at least three surfaces tilted in another direction mergingcontinuously into the main deflecting surface and the boundary surface.12. The vehicle headlamp as claimed in claim 11, wherein the surfacesrespectively merge into one another in a continuously differentiablefashion.
 13. The vehicle headlamp as claimed in claim 10, wherein a basesurface of the lens having no bumps or depressions is regarded asboundary surface.
 14. The vehicle headlamp as claimed in claim 10,wherein the value of the area of a subregion is between a quarter of asquare millimeter and three square millimeters.
 15. The vehicle headlampas claimed in claim 10, wherein the tilt angle between the surfaces ofthe tilted subregion and the neighboring untilted boundary surfacevaries within a subregion, said tilt angle decreasing along a direction(z) of a vertical axis for the headlamp installed in the vehicle. 16.The vehicle headlamp as claimed in claim 11, wherein the surfaces of thetilted subregions constitute parts of lateral surfaces of imaginarycylinders whose axes lie parallel to a base surface of the lens for theheadlamp installed in the vehicle.
 17. The vehicle headlamp as claimedin claim 1, wherein a maximum deflection of a light beam, deflected byan overhead element, in relation to a neighboring light beam that is notdeflected by at least one of the plurality of the overhead element is atleast 5°.
 18. The vehicle headlamp as claimed in claim 1, wherein theboundary surface is a light exit surface of a lens or of a transparentcover pane of the vehicle headlamp.
 19. The vehicle headlamp as claimedin claim 1, wherein the boundary surface is a light entrance surface ofa lens or of a transparent cover pane of the vehicle headlamp.